I. Field of the Invention
The present invention relates to a concept for long-term assessment of the condition of chronically impaired cardiac patients, generally, and particularly pacemaker patients. The concept is based on the integrated presentation of information related to activity level over an extended time period sensed by an implanted cardiac rhythm management system such as a pacemaker device, together with information collected by one or more related sensors presented with annotations of related events as a composite representation.
II. Related Art
Early cardiac pacemakers were used primarily to pace the heart when the normal conduction path from the sinoatrial (SA) node of the heart to the atrial ventricular (AV) node or from the AV node to the ventricles was interrupted. In accordance with these events, the pacemaker was called upon to deliver ventricular stimulating pulses to maintain a predetermined heart rate. More recently, pacemaker technology has become greatly advanced and much more sophisticated. For example, rate adaptive pacing has been used to vary the predetermined rate in accordance with parameters indicative of patient activity level. Pacing has also been used to optimize hemodynamic performance in patients suffering from congestive heart failure (CHF) or other left ventricle dysfunction.
It has also become of interest to monitor the level of activity of a patient over prolonged periods of time as it has become well recognized that the general level of activity and the activity profile are indicative of the well-being and prognosis of the patient. In the case of a CHF patient, for example, a direct correlation has been shown between the level of activity and condition. Historically, such activity has been evaluated using quality of life questionnaires and various exercise tests such as the xe2x80x9cSix-Minute Walk Testxe2x80x9d in which the distance traversed by a patient walking a level path for six minutes is measured. While this and other stress-type tests have provided valuable information, they must be administered by physicians and so require frequent trips to the physicians"" office and they do not provide any on-going monitoring function.
Activity levels can, for example, be measured by means of an accelerometer affixed to the patient which provides data that can be used in assessing the patient""s wellbeing. Such a system is shown in co-pending application Ser. No. 09/076,025, filed May 11, 1998, entitled xe2x80x9cMETHOD AND APPARATUS FOR ASSESSING PATIENT WELL-BEINGxe2x80x9d, assigned to the same assignee as the present application and incorporated herein by reference for any purpose.
That disclosure shows that an accelerometer can be used to determine whether a change in the mode of pacing a CHF patient is beneficial to the overall well-being of the patient. The assessment can be based on intermittent short-term monitoring using an accelerometer sensor and relating it to the level of activity of the patient at that moment.
Pacing devices have also been provided with a memory function to receive and store sensed data relative to cardiac activity which can later be recalled and utilized. Examples of this can be found, for example, in U.S. Pat. No. 5,081,987 to Nigam which uses telemetric transmission of such data for use in a separate external data processor.
While limited practical use has been made of techniques for assessing the well-being of cardiac patients wearing pacing devices, there remains a definite need to monitor patient activity over substantial periods of time to determine longer term trends. In this manner, changes in lifestyles can be seen and overall wellness can be monitored. Trends in patient activity levels indicative of these factors could be presented. It would also be beneficial if additional data regarding events which might affect an evaluation be simultaneously presented and the combination utilized to assess the general condition of the patient and to evaluate outcomes of adjustments in therapy related to the management of the disease.
The present invention involves gathering information and integrating the information to generate an annotated activity chart that enables a physician to track and interpret a CHF patient""s relative wellness. The integrated data of the chart provides information that allows an assessment of outcomes of therapy and changes or adjustments in therapy over time to thereby provide a tool to enable better overall disease management. The invention involves a method of monitoring the activity of a paced patient over an extended period of time thereby noting general changes in lifestyle and relative wellness and displaying data accumulated in that manner, together with annotations indicative of events of interest during the monitored period. A plurality of individual monitoring periods are averaged and recorded and a plurality of successive periods is used to generate an activity chart to show a patient""s overall activity within a longer duration.
The detailed example makes use of the method as applied to a pacing device provided with a plurality of programmable parameters in conjunction with one or more sensors for sensing one or more parameters indicative of the activity level and cardiac function of the patient. Sensor signal data is accumulated and stored in memory over each selected interval or period of interest and a function of that accumulated data is used to represent activity of the patient during that period of interest. Such data records are produced for a sequence of such time periods accumulating sufficient successive relative activity values to produce a data record or chart indicative of trends in the activity level of the patient over a longer duration.
Additional data in the form of annotations recording contemporaneous events which occur during the course of an interval or period of interest are included to provide a more comprehensive representation of wellness data over the longer duration presented in a combined comprehensive representation. The present invention enables evaluation from a single presentation of combined data which may be a histographic representation.
Accordingly, the present invention advantageously provides a method of assessing or evaluating trends in the relative condition or wellness of a chronotropically incompetent patient by observing trends in the activity of the patient over an extended period of time using a single representation of several kinds of data.
The invention also portrays long-term trends in the activity of a patient by charting successive periodic peak or periodically averaged values of activity levels based on shorter durations.
The present invention includes the advantage of including annotated activity chart data to combine a chronology of events of interest with the charted values of activity levels to provide a composite marker channel to aid the physician in interpreting the condition of a patient and assessing therapy outcomes.